The present invention relates to a lock-up control device for a vehicle comprising a transmission and lock-up torque converter.
In the vehicle equipped with a lock-up torque converter, when a lock-up clutch is engaged, the slip in the torque converter is lost, and fuel cost-performance is improved.
However, when the vehicle is coasting with the lock-up clutch engaged (referred to hereafter as xe2x80x9clockup coastingxe2x80x9d), the vehicle body vibrates back and forth when the accelerator pedal is abruptly depressed in a step-shaped manner.
This is because, when the engine torque increases rapidly in a step-shaped manner and this is input to the drive system, the clutch, drive shaft, tires, etc. act as springs and the drive system vibrates as disclosed by JP-A-H8-177540 published by the Japanese Patent Office in 1996.
It is therefore an object of this invention to prevent the above-mentioned vibration from occurring even if the accelerator pedal is largely depressed during lock-up coasting.
In order to achieve above object, the present invention provides a lock-up control device for a vehicle comprising a transmission and a torque converter with a lock-up clutch. The device comprises a sensor which detects a vehicle speed, a sensor which detects either of a throttle opening and accelerator pedal depression amount, and a microprocessor programmed to determine whether an accelerator pedal was depressed in a stepwise manner based on either of the throttle opening and accelerator pedal depression amount, and release the lockup clutch when the vehicle is coasting and the lock-up clutch is engaged, and it is determined that the accelerator pedal was depressed in a stepwise manner. The microprocessor is further programmed to more easily determine that the accelerator pedal was depressed in a stepwise manner the lower the vehicle speed.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.